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In situ near-IR transmittance measurements have been used to characterize the density of trapped electrons in dye-sensitized solar cells (DSCs). Measurements have been made under a range experimental conditions including during open-circuit photovoltage decay and during recording of the IV characteristic. The optical cross section of electrons at 940 nm was determined by relating the IR absorbance to the density of trapped electrons measured by charge extraction. The value, σ n ) 5.4 × 10 -18 cm 2 , was used to compare the trapped electron densities in illuminated DSCs at open and short circuit in order to quantify the difference in the quasi Fermi level, ∆ n E F under the two conditions. It was found that ∆ n E F for the cells studied was 250 meV over wide range of illumination intensities. IR transmittance measurements have also been used to quantify shifts in conduction band energy associated with dye adsorption.

Session identification is a common strategy used to develop metrics for web analytics and behavioral analyses of userfacing systems. Past work has argued that session identification strategies based on an inactivity threshold is inherently arbitrary or advocated that thresholds be set at about 30 minutes. In this work, we demonstrate a strong regularity in the temporal rhythms of user initiated events across several different domains of online activity (incl. video gaming, search, page views and volunteer contributions). We describe a methodology for identifying clusters of user activity and argue that regularity with which these activity clusters appear implies a good rule-of-thumb inactivity threshold of about 1 hour. We conclude with implications that these temporal rhythms may have for system design based on our observations and theories of goal-directed human activity.